Search Results (209)

Critical illness myopathy (CIM) is linked to mechanical ventilation and complete mechanical muscle silencing in intensive care unit (ICU) patients. Limb muscles show atrophy and declined specific single fibre force through altered protein turnover and diminished myosin-to-actin ratios. A rat ICU model reproducing preferential myosin loss and specific force decline in limb muscle was used to assess myofibrillar remodelling. After 5 or 10 days of ICU intervention, single extensor digitorum longus (EDL) and soleus muscle fibres were imaged using label-free, Second Harmonic Generation (SHG) microscopy, followed by quantitative 3D morphometry. The degree and severity of deranged myofibrillar architecture was assessed through (i) 2D and 3D Cosine Angle Sums (CAS2D/CAS3D) and (ii), Vernier Densities (VD) parameters. A progressively declining myofibrillar order was seen by dropping CAS2D/3D and increasing VD values during ICU intervention, reflecting angular and axial register deviations. Effects of chaperone co-inducer BGP-15, dissociative glucocorticoid Vamorolone (VBP-15) or its parent compound Prednisolone on myofibrillar architecture were explored. Both BGP-15 and VBP-15 modulated the progression of myofibrillar disorder seen during ICU intervention alone: For soleus fibres, BGP-15 maintained structural integrity at day 5 but not at day 10, while even worsening myofibrillar order in the EDL. VBP-15 reversed atrophy at day 10 in soleus but not in EDL fibres. Our study is the first to quantify myofibrillar remodelling in limb muscle fibres during ICU intervention in 3D and provides exploratory assessment of BGP-15 and VBP-15 treatments on aberrant remodelling in CIM. Full article

We present a method for quantifying ultrashort pulse-shape instability in a train of pulses using multi-shot second-harmonic-generation frequency-resolved optical gating (SHG FROG). All versions of multi-shot FROG have previously shown the ability to qualitatively distinguish stable from unstable pulse trains, as systematic differences appear between measured and retrieved FROG traces when instability is present. This has proved possible because the recently introduced retrieved-amplitude N-grid algorithmic (RANA) approach provides highly reliable pulse retrieval, even for unstable pulse trains and in the presence of noise, thereby eliminating the possibility that algorithm stagnation, which also yields such systematic differences, could be confused for such instability. In other words, RANA’s excellent performance ensures that any non-random discrepancies between measured and retrieved FROG traces reflect physical pulse-shape instability rather than algorithmic stagnation. To quantify such instability, we now introduce an instability parameter, $R$. It involves an extension of the well-known statistical “Runs” test, which has been used for decades to test for systematic error in fits to one-dimensional (1D) data. A runs test counts the “runs”—consecutive points in the plot of the difference between the data and fit with the same sign (+ or −), yielding an evaluation of the goodness of the fit, largely independent of random error. Specifically, the more runs, the better the fit. However, because FROG traces are functions of two variables, we must extend the usual 1D runs test to two dimensions, that is, to enumerate the 2D runs—“hills” and “valleys” in the difference between measured and retrieved 2D FROG traces. Many small 2D runs indicate only random noise-like differences, that is, a good fit, and, hence, a stable pulse train, whereas few large runs reflect systematic error, that is, a poor fit, and, hence, pulse-shape instability. Finally, because random noise could contribute numerous meaningless runs in the wings of a FROG trace, where the intensity is near zero, we must also weight each hill and valley by its average measured trace intensity in order to minimize its effects. We show that R is intuitive and reasonable and, in addition, is independent of pulse complexity and trace size. As a result, it provides a clear metric of pulse-shape stability vs. instability. Full article

High-power 355 nm ultraviolet (UV) lasers, leveraging their short wavelength, high photon energy, and high absorption across a broad range of materials, have become indispensable light sources for precision manufacturing, semiconductor processing, and laser direct imaging (LDI). In this paper, we demonstrate a high-power 355 nm UV laser system based on a narrow-linewidth polarization-maintaining (PM) Yb-doped fiber laser and cascaded frequency conversion. A single-frequency semiconductor laser is employed as the seed source, with its spectral linewidth broadened to 0.32 nm (full width at half maximum, FWHM) via phase modulation to suppress stimulated Brillouin scattering (SBS). Through a PM master oscillator power amplifier (MOPA) architecture, a maximum average output power of 899 W at 1064 nm is achieved with a beam quality factor of M² = 1.12 (M²_x = 1.11, M²_y = 1.13). By employing lithium triborate (LiB₃O₅, LBO) crystals for extracavity cascaded second-harmonic generation (SHG) and sum-frequency generation (SFG), a maximum green output power of 613.7 W at 532 nm is obtained, corresponding to a SHG conversion efficiency of 68.2%, and a maximum UV output power of 227.1 W at 355 nm is achieved, with a total conversion efficiency of 25.2%. At the maximum output power, the UV beam quality factors are M² = 1.16 (M²_x = 1.24 and M²_y = 1.09), and the power fluctuation is better than ±1.5% root-mean-square (RMS) over 8 h of continuous operation. These results indicate that the cascaded frequency conversion approach based on narrow-linewidth PM fiber lasers possesses the capability for further scaling to higher-power single-path high-brightness UV output and can provide high-brightness UV sources for applications such as flexible printed circuit (FPC) laser cutting, flat-panel display laser direct imaging, and semiconductor wafer scribing. Full article

We report a new approach to enhance the photonic response of thin-film topological insulator Bi₂Se₃ by significantly reducing twin domains and antiphase disorder. The strategy employs closely lattice-matched trigonal substrates combined with surface structuring to preferentially seed a single rotational domain before epitaxy. Characterization using optical second harmonic generation (SHG), nonlinear optical tensor analysis, X-ray diffraction, and atomic force microscopy confirms the near-single crystal Bi₂Se₃ heteroepitaxial layers. These results show a clear six-fold symmetric sin²(3ϕ) SHG pattern at normal incidence, and a vanishingly small 100-to-1 peak-height ratio from X-ray pole-scans showing negligible twinning. These results show that this approach can yield near perfect single crystal heteroepitaxial Bi₂Se₃ whose photonic properties converge to those of bulk-grown single crystals. Full article

Cellular senescence and polyploidy are fundamental stress responses that shape cancer progression and therapeutic outcomes. While senescence initially suppresses tumor growth, senescent cells accumulate in aging and therapy-exposed tissues and actively remodel the tumor microenvironment through the senescence-associated secretory phenotype (SASP) and extracellular matrix (ECM) reorganization. Senescent stromal cells increase collagen deposition and generate disordered matrix architectures, as evidenced by enhanced second harmonic generation (SHG) signal and increased anisotropic variation across in vitro systems, 3D co-culture models, and fibrotic lung tissues. These biochemical and mechanical alterations promote cancer cell plasticity and create conditions permissive for disease progression. Polyploid giant cancer cells (PGCCs) are a rare but highly resilient cancer cell population enriched under genotoxic stress. PGCCs arise through mitotic failure, including mitotic slippage and cytokinesis defects, and can survive chemotherapy and radiation due to their altered cell-cycle regulation. Emerging evidence indicates that senescence-driven microenvironments promote the formation of PGCCs and multinucleated cells, linking ECM remodeling and mechanical stress to polyploidization. Functionally, PGCCs exhibit abnormal cytoskeletal and nuclear mechanics that support migratory persistence and enable survival within hostile tumor environments. In addition, PGCCs can promote the survival of neighboring cancer cells during treatment, suggesting a stromal-like role in establishing therapy-resistant niches. These cells can persist in a dormant state and later generate proliferative progeny, contributing to tumor recurrence and metastasis. Together, these findings support a model in which senescent niches may promote PGCC formation, persistence, and tumor repopulation. Targeting both senescence-associated microenvironments and PGCC-specific survival mechanisms may improve long-term therapeutic outcomes. Full article

We demonstrate efficient and thermally stable second-harmonic generation (SHG) in x-cut thin-film lithium tantalate (TFLT) ridge waveguides via modal phase matching (MPM). The experimental characterizations reveal a normalized conversion efficiency (NCE) of 17.2% W⁻¹ cm⁻² in a 4 mm long waveguide. Notably, the device exhibits a temperature-dependent phase-matching wavelength slope of 0.007 nm/°C, which shows a two-orders-of-magnitude improvement in thermal stability over conventional periodically poled lithium niobate/lithium tantalate optical devices. Our work indicates that MPM in TFLT is an attractive strategy for integrated nonlinear optical applications, particularly for the on-chip frequency conversion of both classical and quantum light signals without on-chip domain-poling processes. Full article

High quality factor (Q factor) resonant metasurfaces enable efficient mid-infrared (MIR) upconversion, yet their narrow operating bandwidths severely limit practical broadband detection and imaging applications. Although high Q magnetic toroidal dipole (MTD) modes exhibit outstanding momentum space ($k$-space) stability in linear optics, their application in nonlinear processes has primarily been confined to degenerate second-harmonic generation (SHG), leaving complex non-degenerate processes such as sum-frequency generation (SFG) largely unexplored. Here, we propose a tunable MIR upconversion platform based on an all-dielectric gallium phosphide (GaP) dimer metasurface. Breaking the in-plane symmetry to trigger Brillouin zone folding excites robust MTD quasi-guided modes (MTD-QGM), tightly confining the locally enhanced optical fields within the highly nonlinear GaP nanostructure. Synchronizing this high Q resonance with a spatially overlapping pump mode yields an exceptional SFG conversion efficiency of $7.9\times {10}^{-4}$, successfully translating a 3101.8 nm MIR signal to the 903 nm near-infrared band. Crucially, the intrinsic $k$-space stability of the MTD-QGM enables continuous, broadband upconversion through simple angle tuning. This mechanism effectively overcomes the narrow-band limitations characteristic of typical symmetry-protected resonators, establishing a robust paradigm for room-temperature MIR detection. Full article

Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under electric dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high-temperature fabrication processes. In this work, heterostructures made of two distinct amorphous materials, namely SiO₂ and TiO₂, were prepared through plasma-enhanced atomic layer deposition (PEALD) with deposition temperature of 100 °C. By using the uniaxial dispersion model, we characterized the form birefringence of the deposited films, which can play a crucial role for the phase-matching condition in nonlinear waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective bulk second-order susceptibility, ${\chi }_{zzz}^{\left(2\right)}$ = 1.30 ± 0.13 pm/V, at a wavelength of 1032 nm. Noteworthy, we observed strong SHG signals from two-component nanolaminates, which are several orders of magnitude larger than those from single layers. The SHG signals from our samples only require the broken inversion symmetry at the interface. Here, optical properties of nanocomposites can be precisely engineered using the promising PEALD technology. Full article

High-order Poincaré sphere (HOPS) beams have attracted tremendous interest due to their complex polarization and phase characteristics. However, manipulating the second harmonics generation (SHG) of HOPS beams is still challenging. Here, we developed a vector-coupled wave model to predict petal-shaped intensity patterns and reveal a linear correlation between petal number and topological order (n = 2 → 4). Moreover, we experimentally investigated the multidimensional regulation of SHG in HOPS beams through tailored phase-matching strategies. By employing three distinct configurations—(i) type-I phase matching, (ii) type-II phase matching, and (iii) orthogonally arranged BBO crystals based on Type-I phase matching—we establish a comprehensive framework for controlling the spatial and polarization properties of SHG in n = 2 HOPS beams. These results advance the manipulation of structured light in nonlinear optics, providing insights for optimizing applications in optical communication and polarization imaging. Full article

We propose a silicon carbide (3C-SiC) periodic grating structure based on quasi-bound states in the continuum (q-BICs), which is used to significantly enhance the second-order optical nonlinear effect, including second-harmonic generation (SHG) and sum-frequency generation (SFG). By introducing a four-segment sub-wavelength grating on the SiC thin film and tailor the dimension, the structure successfully excites two q-BIC modes with ultra-high Q factor (resonant wavelengths at 1713.2 nm and 1804.6 nm respectively), realizing enhanced localization and nonlinear interaction of the strong light field. The simulation results show that under oblique incidence, the structure significantly enhances SFG efficiency and exhibits strong robustness to variations in key structural parameters. In addition, the study also reveals the coexistence of forward and backward SHG, and resonant wavelength tuning can be achieved by adjusting the structure dimension. This work not only provides a new path to enhance the nonlinear conversion efficiency of SiC thin films and solve the problem of difficult phase matching, but also lays the theoretical and technical foundation for the development of compact, efficient and integrated SiC-based nonlinear photonic devices. Full article

Interest in non-centrosymmetric crystalline materials exhibiting second harmonic generation (SHG) has increased due to their potential applications in optical sensing and biosensing. Saccharide-based metal complexes are particularly attractive systems, as chiral sugars can promote non-centrosymmetric crystal packing. In this work, a new lanthanum–β-d-fructose compound, [La(C₆H₁₂O₆)(H₂O)₅]Cl₃ (LaFRUCl), was synthesized using a simple and low-cost method and characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ and consists of infinite (La³⁺–fructose)_n chains extending along the [001] direction, forming a one-dimensional Metal–Organic Framework. The nonlinear optical response was evaluated using the Kurtz–Perry powder technique with a Nd:YAG laser (1064 nm) and compared to a sucrose reference. The measured SHG efficiency is comparable to that of previously reported alkaline earth metal–sugar analogs. While the compound’s SHG emission is significant, evaluation of its structural stability under aqueous or physiological conditions is be required before considering biological applications. Full article

Molybdenum tellurite compounds have attracted increasing interest as promising nonlinear optical (NLO) materials, yet their microscopic second-harmonic generation (SHG) mechanisms remain unclear. In this work, the electronic structures and SHG responses of ATeMoO₆ (ATM, A = Mg, Cd, Zn) are systematically investigated using first-principles calculations combined with atom response theory. The results show that the SHG responses are mainly governed by the occupied nonbonding O 2p states and the unoccupied Mo 4d and Te 5p states. Our atom response theory analysis reveals that a strong synergistic effect between stereochemically active lone pairs (SCALPs) on Te atoms and nonbonding O 2p states critically enhances the SHG response in ZnTM and MgTM. In contrast, the relative weaker Te SCALPs in CdTM fail to provide a comparable contribution, leading to its lower SHG performance. The structure group analysis reveals that MoO₄ units dominate the SHG response, while TeO₄ units provide secondary contributions. Moreover, group dipole moments are found to be insufficient to explain the SHG behavior. These findings provide microscopic insights into SHG origins and offer guidance for NLO material design. Full article

Wool fibers undergo significant structural changes during industrial stretching, which directly impact their mechanical properties and textile performance, making monitoring of the stretching process essential for optimizing wool products. In this study, we demonstrate the effective use of polarized second harmonic generation (P-SHG) imaging for monitoring the wool fiber stretching process. P-SHG is highly sensitive to non-centrosymmetric structures, enabling clear observation of changes in α-keratin alignment and the reconstruction of cortical interfaces during stretching. Quantitative P-SHG analysis revealed a significant decrease in the effective pitch angle (θ_e) from 54° ± 1° to 33° ± 3° after stretching, confirming the dipole orientation changes in keratin molecules. These findings were further validated through additional characterization techniques, including scanning electron microscopy (SEM), polarizing optical microscopy (POM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The results show that the industrial stretching process of wool alters the morphology at the surface scale, enhances the alignment of macroscopic fibers, and induces a transition from α-helix to β-sheet. Our technique is simple, effective, and capable of in situ monitoring of the structural changes in wool fibers, making it highly promising for applications in the wool industry. Full article

Background and Objectives: Extracellular matrix (ECM) and collagen remodeling contribute to chronic kidney disease (CKD) progression and vascular access dysfunction. Conventional histological techniques rely on staining and provide limited sensitivity for detecting early or subtle ECM alterations. Nonlinear optical imaging modalities, including second-harmonic generation (SHG), third-harmonic generation (THG), and multiphoton fluorescence (MPF) microscopy, enable label-free, high-resolution visualization of fibrillar collagen and may offer additional structural information. This study aimed to evaluate the added value of nonlinear imaging beyond conventional histology for assessing ECM remodeling in renal and vascular tissues. Materials and Methods: A systematic literature review was conducted in accordance with the PRISMA 2020 guidelines. PubMed and Web of Science were searched for studies published between 1 January 2015, and 4 April 2025, investigating ECM or collagen remodeling in renal or vascular tissues using SHG, THG, or MPF microscopy. After screening 115 records, 10 studies were included in the qualitative synthesis. In addition, representative SHG, THG, and MPF images of excised human arteriovenous fistula (AVF) tissue were acquired as illustrative feasibility examples to demonstrate the application of these imaging modalities. The use of human tissue was approved by the Vilnius Regional Biomedical Research Ethics Committee (approval No. 2022/6-1443-917). Results: The included studies demonstrated that nonlinear microscopy enables label-free assessment of collagen density, organization, and fiber orientation. SHG imaging differentiated healthy from diseased tissues and has been reported to support fibrosis assessment and staging in preclinical and selected clinical studies and revealed microstructural remodeling patterns not readily detected by conventional histology. The illustrative AVF images demonstrated collagen disorganization consistent with patterns reported in the reviewed literature and are presented solely to demonstrate imaging feasibility, without implying disease phenotype or clinical outcome associations. Conclusions: Nonlinear optical microscopy provides complementary structural information on ECM organization that is not accessible with standard histological techniques. Further validation and methodological standardization are required to support its broader application in clinical nephrology and vascular medicine. Full article

We report a dispersion-controlled Yb-doped fiber chirped pulse amplification (CPA) system incorporating a tunable chirped fiber Bragg grating (CFBG) stretcher and a single-grating transmission compressor for dynamic compensation of power-dependent nonlinear effect. During the pulse amplification, the CFBG introduces adjustable third-order dispersion (TOD). By tuning the initial TOD provided by CFBG from −0.1965 ps³ at 2.37 W to −0.1791 ps³ at 9.65 W, residual TOD is efficiently compensated with the power-dependent nonlinear effect. As a result, by optimizing the dispersion balance at each output power, nearly constant femtosecond pulses with a duration of 250 fs are obtained over the entire power range, confirming effective control of nonlinear and dispersive effects in the amplification. The high-quality 1030 nm pulses enable efficient second-harmonic generation (SHG) in a type-I BBO crystal, producing 3.56 W femtosecond output at around 515 nm with a pulse duration of 190 fs, close to the Fourier transform limit. These results demonstrate a robust approach to generating high-power and temporal coherent ultrafast pulses suitable for precision micromachining and two-photon polymerization. Full article